This invention relates to the angled injection of a gas such as cooling air and, more particularly, to an injection apparatus and its fabrication.
It is sometimes necessary to inject a gas from a thin-walled gas plenum, through a relatively long passage, and at an inclined injection angle into a space. As an example, in the tubomachinery of a gas turbine engine, cooling air is injected at an inclined angle from an annular plenum into the cavity between the plenum and a rotating shaft. The cooling air must be injected at an angle to the axial direction to avoid turbulence that would lead to local hot spots, and the air must flow down a tube to ensure that it is flowing in a stable manner in the intended direction.
A simple hole or orifice in the wall of the plenum does not produce the desired inclined flow direction and flow uniformity. A fitting with a hole therein may be welded into the wall of the plenum, but the welding of the fitting is expensive and time-consuming.
In another approach to the injection problem, the wall of the plenum is made sufficiently thick, and inclined passages are drilled at the required locations and angles. This solution is operable but requires the use of a thick-walled plenum that adds unnecessary weight to the structure. In yet another approach, a ring having the necessary passages drilled therein is welded into the wall of the plenum to form part of the wall. This approach is operable but costly to implement because of the required welding and also adds unnecessary weight. Changing the sizes and orientations of the passages is difficult, and requires that the ring be replaced.
None of the existing solutions to the gas injection problem has proved fully satisfactory. There is a need for an improved approach to the injection of gas from a plenum. The present invention fulfills this need, and further provides related advantages.
This invention provides a gas injector system and a method for its fabrication. The gas injector system works with gas supplied through a plenum, such as a thin-walled plenum. The gas injector provides an elongated gas flow passage with an inclined injection angle. A wide variety of shapes, sizes, and arrangements of gas flow passages may be utilized and fabricated. The gas injector is fabricated separately from the plenum and then affixed to the plenum. It may also be detached from the plenum and replaced if necessary.
A gas injector system comprises a plenum having a plenum wall with an exterior surface, a local tangential direction parallel to the exterior surface, and a local normal direction perpendicular to the exterior surface. The plenum may be of any thickness, but typically is relatively thin sheet metal. There is a plenum opening in the plenum wall. An injector is positioned at a location overlying the plenum opening. The injector comprises an injector block affixed to the plenum wall, a joint between the injector block and the plenum wall, and an injector passage extending through the injector block from an injector passage inlet to an injector passage outlet. The injector passage outlet is oriented at an injection angle of more than 0 degrees away from the local normal direction and toward the local tangential direction. The injector passage inlet is in registry with the plenum opening. In a typical embodiment, the plenum has a plurality of openings in the plenum wall and a respective injector for each of the openings.
In one form, the injector passage is substantially straight and of constant diameter. In other forms, however, the injector passage may be curved and/or of a non-constant diameter, non-circular cross section, or in the form of a nozzle. There may be one or more than one injector passage in the injector block. The injection angle of gas leaving the injector passage(s) may be at any operable orientation, but typically is from about 50 degrees to about 70 degrees from the local normal direction. The joint is preferably a brazed joint for high-temperature applications, or an adhesive joint for low-temperature applications, both of which are more convenient and less expensive than the welding used in conventional approaches.
In an application of particular interest to the inventor, the injector system injects gas into the cavity between a gas plenum and a rotating turbomachinery shaft, so that the gas is injected toward the direction of rotation. In this embodiment, a gas injector system comprises an annular plenum having an annular centerline, a plenum wall with an exterior surface, a local circumferential tangential direction parallel to the exterior surface, and a local normal direction perpendicular to the exterior surface. A plurality of plenum openings are formed in the wall of the annular plenum, the plenum openings being spaced along a circumferential band of the annular plenum. The circumferential band of the annular plenum typically faces inwardly toward the annular centerline. The injector system includes a plurality of injectors, each injector being positioned at a location overlying one of the plenum openings. Each injector comprises an injector block affixed to the plenum wall, a joint between the injector block and the plenum wall, and an injector passage extending through the injector block from an injector passage inlet to an injector passage outlet. The injector passage outlet is oriented at an injection angle of more than 0 degrees away from the local normal direction and toward the local circumferential tangential direction.
The gas injector system is prepared by fabricating an injector block having an injector passage therethrough extending through the injector block from an injector passage inlet to an injector passage outlet, providing a gas plenum having a plenum wall with an exterior surface and an opening through the plenum wall, and affixing the injector block to the plenum wall with the injector passage inlet in registry with the opening through the plenum wall. At a later time, the injector block may be removed if desired, and a new injector block with a different configuration of the injector passage(s) affixed to the plenum wall. The injector block is conveniently cast with the injector passage defined therein, or the injector passage may be machined into the injector block. Casting of the injector block with one or more integral injector passages allows great flexibility in the selection of the shape, size, and form of the passages.
The present approach provides a gas injector system which is conveniently and inexpensively fabricated. Gas may be injected as required from a plenum, even a thin-walled plenum. Other features and advantages of the present invention will be apparent from the following more detailed description of the preferred embodiment, taken in conjunction with the accompanying drawings, which illustrate, by way of example, the principles of the invention. The scope of the invention is not, however, limited to this preferred embodiment.